Sheet casting from polymerizable materials containing pearlescent pigments



Jan. 19, 1960 w. K. FISCHER SHEET CASTING FROM POLYMERIZABLE MATERIALS CONTAINING PEARLESCENT PIGMENTS Filed Dec. 51. 1957 22 g/ K/J INVENTOR W/Zl/A/V KA/RI. F/JCHER Jm WJW ATTORNEY 2,921,346 SHEET CASTING FROM POLYMERIZABLE MATE- RIALS CONTAINING PEARLESCENT PIGMENTS William K; Fischer, Woodbury, Conm, assignor to United States Rubber Company, New York, N.Y., a corporation of New Jersey Application December 31, 1957, Serial No. 706,310 6 Claims. (Cl. 18-57) This invention relates to a method of forming unsupported plastic sheets from liquid polymerizable materials containing flake pigments. The sheets herein contemplated are well adapted for use as material from which buttons are manufactured.

One of the most important phases of the operation in manufacturing sheets from plastics is the use of pigments to obtain pleasing color effects. This is so mainly because much of the trade is established upon the unusual ability of plastics to portray color. However, where pearlescent pigment flakes are used, considerable objection is encountered notwithstanding that the plastic compositions have excellent clarity and brilliance. Thus, an insuflicient percentage of the pearlescent flakes may not be oriented to lie in the plane of the sheet; that is they may be up-ended to show a lusterless and unpleasing edge. Much of this results from the inability of the methods heretofore used to properly orient the pigment flakes before the resin is cured or set. For example, in a conventional casting process, resin compositions containing the reflective flakes are poured into a mold which is rather high in its vertical dimension. The only force tending to orient the flakes is the flow of the composition which must be effective in the time the composition flows from the dispensing receptacle into the casting mold. Gelation of the resin must begin immediately or very shortly after, since the flakes will quickly reorient out of the plane of the sheet to be formed. Obviously it is diificult to obtain with any regularity satis factory sheets by this process, and the size of the sheet which can be formed is limited to the size of the mold. The casting method also has the disadvantage that the thickness of the sheet is limited, since in the case of thick sheets the flakes tend to orient perpendicular to the plane of the sheet. This method has the further disadvantage that surfaces of the mold or form that contact the resin composition must be highly polished and coated with a suitable lubricant material to prevent sticking of the resin to the mold. Another method is to line the interior of the cell with an envelops of cellophane or other insoluble film. This coating envelope must later be removed. Unless it is applied properly no benefits are secured and, in fact, detrimental effects take place in that the surface appearance of the sheet will be marred by wrinkles in the lining.

The object of this invention is, therefore, to provide a process which avoids the disadvantages of the above processes and has steps correlated with liquid polymerizable compositions containing flake pigments which will produce sheets containing a maximum orientation of the flakes. In the drawings:

Fig. l is an elevational View of the apparatus shown schematically for carrying out the various steps of making a sheet containing pearlescent or metallic flake pigments;

Fig. 2 is a plan View of the apparatus of Fig. 1.

Fig. 3 is a sectional view taken on the line 33 of Fig. 2; I

Fig. 4 is a sectional view taken on the line 44 of Fig. 2, and

Fig. 5 is a perspective view of a sheet made according to the invention.

68 Pfittiflt F Patented Jan. 19, 1960 According to the invention, the sheets, in general, are formed by first providing a surface of a convenient carrier or base with a fluid coating of pigmented resinous material which is to form the sheet. This is a plastic material in liquid form containing suspended flake pigments. The consistency of the coating material is regulated to suit the conditions as is well understood by those skilled in the the art. It is desirable that the surface of the carrier that is to be coated to be smooth to avoid reproduction of unwanted imperfections or formation of bubbles which may occur around pits. The carrier must be flexible and readily separable from the sheet on solidification of the coating material. Sheets of cellophane or polyester film (Mylar) are preferred for the purpose, since they fulfill these requirements and are relatively inexpensive.

After the coating is applied, the carrier is folded into a web of a generally U-type cross-section having the coating within its trough and then subjected to pressure by passing it between suitably separated restricting surfaces or platens. The pressure from the platens causes the coating material to flow transversely thereby orienting the flakes in the direction of the flow which is the plane of the sheet to be formed. It is preferred that the restricting platens be positioned vertically since the folded carrier passing between the platens is then vertical and thus the depth of the material. in which the flakes are suspended is relatively large. This provides an opportunity for the force of gravity to aid in orienting the flakes.

Immediately upon orientation of the flakes, the coating material is gelled to fix the flakes permanently in their oriented position. This is achieved by passing the carrier between heating platens aligned with the pressure platens. The heating platens are preferably spring mounted to compensate for shrinkage of the plastic. When a sheet is to be used for making buttons, it is usually desirable to only partly cure the plastic or just sufliciently to fix the flakes permanently in position. The plastic is then quite rubbery and permits stamping of blanks from the sheet without fracturing. After full curing, the blanks can be machined, drilled and polished.

Some manufacturers prefer to machine buttons from fully cured plastic sheet. This may be accomplished in my method by properly adjusting amount of catalyst and curing temperature. Thus in Figure 1 instead of cooling platen #23, it may be heated.

The materials used in the process are all well known in the art and a wide variety of them may be employed, depending largely on the physical properties desired in the final product. The microscopic pigment flakes can be natural of synthetic materials insensitive to the plastic. Thus, specially prepared fish scales, and the various micas are suitable natural flake materials, whereas, aluminum, lead carbonate and the like in flake form are good examples of usable synthetics.

The sheet forming plastics likewise can be any of a wide variety. Typical would be an unsaturated polyester resin of the type that will cure with a vinyl type of cross linking agent, such as styrene. Inhibitors, promoters and catalysts likewise are utilized as the need arises.

In the practice of the invention a batch of the material is first prepared. Such a batch has been'used in which mica flakes were suspended in a polyester resin. The resin was prepared by mixing one mol each of maleic and phthalic anhydrides with two mols of propylene glycol and heating the resulting mixture to about 200 C. for 4 to 5 hours during which time water was driven off under a blanket of carbon dioxide until an acid number of about 40 was reached. The resulting polyester resin was allowed to cool to 160 C. and an inhibitor, hydroquinone in the proportion of parts per million, was added to prevent premature gelation and permit delayed use of the resin. After the resin had further cooled to about 100 C. a copolymerizable monomer was added, as one part of styrene to two parts of resin. Obviously variations are permissible in the ingredients and their proportions depending on conditions and desired characteristics of the resulting sheet.

Just prior to subjecting the resin, such as the one described above, to the sheet forming operation, the pigment flakes were added. The percentage of flakes in the resin exceeded one-eighth of one percent. The amount used of course depends again on the transparency desired. An increase in the percentage of flakes used increases the opaqueness of the resulting sheet.

When it is desired or necessary to use a catalyst and promoter, they are added to the resin after the flake pigments. The amount and the type of each is well known in the art. Some of the catalysts that are suitable include methyl ethyl ketone peroxide, benzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, etc.; whereas, some of the usable promoters include cobalt naphthenate, zinc chloride, diethyl aniline, dimethyl aniline, and dodecyl mercaptan.

In the drawing, I have schematically illustrated the apparatus and method whereby a sheet containing flaked pigments 11 may be continuously made from the materials described above. According to the invention, the liquid mixture generally indicated with the numeral 12, is applied as a coating 13 on a moving carrier 14, preferably a sheet of cellophane supplied from a roll 15, that is approximately twice as wide as the sheet to be produced. The coating 13 is slightly more than half the thickness of the desired sheet 10 and is readily applied by dispensing the mixture 12 from the hopper 16 that is supported over the cellophane carrier 14. Dispensing is done from a spout 17 of the desired width, which is generally less than the Width of the carrier 14. Carrier 14 is doubled by folding it longitudinally, after being coated, in a generally U-shape with the coating 13 in the trough, and is advanced in the direction of the arrow between two restricting platens 18, 18 that are rigidly mounted in a vertical position and suitably spaced to produce the desired thickness in the finished sheet 10. Conveniently the platens 18, 18 are flared as shown at 19, 19, the point at which the carrier 14 enters the platens, to help fold the carrier 14. As shown, the restricting platens 18, 18 form an open top open ended mold, that exerts pressure causing the coating to flow somewhat toward the open sides of the-molds and compact it into a single sheet double its original thickness. The pressure along with the flow of the material between the platens '18, 18 orients the flakes 11 in the plane of what is to be the sheet 10. In this respect, the fact that the material is passed through the restricting platens in a vertical position, the depth of the material is at a maximum and force of gravity is effective in aiding the orientation of the flakes 11.

The folded cellophane carrier 14 supports and conveys the flake-oriented, ungelled mixture into an adjacent heating chamber 20 maintained at the proper temperature. The temperature may be varied from 70 to 190 F., dependent upon the type and amounts of catalyst and promoter employed, to gel the coating 13 and fix the flakes 11 as oriented. The coating 13 upon gelling forms the sheet 10.

The heating chamber 20 is also preferably a pair of vertically positioned platens 21, 21 aligned with the restricting platens 18, 18. Springs 22 mounted on the outside of the platens 21, 21 tend to keep a slight compressive force on the sheet 10 and thus adjust the platens 21, 21 to the expansion due to heating and the subsequent sheet shrinkage resulting from curing.

A cooling chamber 23 may be provided in the form of platens similar to those of the heating chamber 20 where it is desired to better control the degree of cure of the sheet 10.

The carrier 14 is preferably separated from the sheet 10 by slitting it longitudinally at the underside of the trough and then peeling away the resulting strips 24, 24 to the sides of the sheet 10 on rollers 25, 25. A knife 26 with its blade directed upwardly and disposed at the exit end of the cooling chamber 23 may be used for the slitting operation.

Desired lengths of the sheet 10, free of the cellophane carrier 14, are then cut from the continuous length as it leaves the cooling chamber 23. However, it is within the principle of the invention to cut the sheet into suitable lengths without first removing the cellophane carrier 14 when the sheets are to be stored. In this respect the cellophane carrier 14 acts as a protective covering.

It can thus be seen that I have invented a process whereby a sheet having flaked pigments can be made continuously of unlimited length.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. The method of making sheets having flake-type pigments oriented in substantially the plane of the sheet comprising, forming a suspension of said pigments in a polymerizable liquid thermosetting composition, applying a deposit of said suspension on a surface of a relatively wide, flexible, ribbon-like conveyor adaptable for ready separation from said sheet, folding said conveyor into a deep, narrow U-shaped trough having said suspension in said trough, moving said conveyor between opposed restraining platens, thus applying a pressure on said suspension causing said pigment flakes to orient parallel to said platens, applying heat to said suspension while said pigment flakes are so oriented to effect a controlled degree of polymerization of said composition and to fix said pigment flakes in said oriented position, applying subsequent cooling to halt polymerization and stripping said conveyor from the sheet thus formed.

2. A continuous method of making sheets having flaketype, pearlescent pigments oriented in substantially the plane of the sheet from a suspension of flake-type pigments in a polymerizable liquid thermosetting composition comprising, continuously casting said suspension on a relatively wide, moving, flexible, ribbon-like conveyor adapted for stripping from the formed sheet, continuously drawing said conveyor between opposed restraining platens causing said conveyor to fold into a deep, narrow U-shaped trough with said suspension in said trough and to orient said flakes parallel to said platens, applying heat to said suspension while said pigment flakes are so oriented to effect formation of said sheet by polymerization of said composition and to fix said pigment flakes in said oriented position, applying subsequent cooling to halt polymerization and stripping said conveyor from the sheet thus formed.

3. The method of claim 2 in which said heat is applied by continuously passing said conveyor with said composition containing the oriented pigments between opposed heating platens.

4. The method of claim 2 in which said cooling is applied by continuously passing said sheet after polymerization of said composition between opposed cooling platens.

5. In the method of claim 2, applying pressure to said sheet during said application of heat to compensate for volume variations during said polymerization.

6. In the method of claim 2, orienting said U-shaped trough so that its axis is vertical.

References Cited in the file of this patent UNITED STATES PATENTS 2,345,013 Soday Mar. 28, 1944 2,500,728 Williams Mar. 14, 1950 2,668,328 Porter Feb. 9, 1954 FOREIGN PATENTS 614,198 Great Britain Dec. 10, 1948 

